Thermally Reentrant Crystalline Phase Change in Perovskite‐Derivative Nickelate Enabling Reversible Switching of Room‐Temperature Electrical Resistivity

Reversible switching of room‐temperature electrical resistivity due to crystal‐amorphous transition is demonstrated in various chalcogenides for development of non‐volatile phase change memory. However, such reversible thermal switching of room‐temperature electrical resistivity has not reported in transition metal oxides so far, despite their enormous studies on the electrical conduction like metal‐insulator transition and colossal magnetoresistance effect. In this study, a thermally reversible switching of room‐temperature electrical resistivity is reported with gigantic variation in a layered nickelate Sr(2.5)Bi(0.5)NiO(5) (1201‐SBNO) composed of (Sr(1.5)Bi(0.5))O(2) rock‐salt and SrNiO(3) perovskite layers via unique crystalline phase changes between the conducting 1201‐SBNO with ordered (O‐1201), disordered Sr/Bi arrangements in the (Sr(1.5)Bi(0.5))O(2) layer (D‐1201), and insulating oxygen‐deficient double perovskite Sr(2)BiNiO(4.5) (d‐perovskite). The O‐1201 is reentrant by high‐temperature annealing of ≈1000 °C through crystalline phase change into the D‐1201 and d‐perovskite, resulting in the thermally reversible switching of room‐temperature electrical resistivity with 10(2)‐ and 10(9)‐fold variation, respectively. The 1201‐SBNO is the first oxide to show the thermally reversible switching of room‐temperature electrical resistivity via the crystalline phase changes, providing a new perspective on the electrical conduction for transition metal oxides.